The field of the invention is that of L-head internal combustion engines. More particularly, the invention relates to L-head internal combustion engines having a cast cylinder assembly and an intake cross-under passage.
One arrangement of a prior art L-head internal combustion engine, which is sometimes referred to as a side valve engine, comprises a crankshaft disposed vertically which reciprocates with a horizontally disposed piston. The cylinder includes intake and exhaust valve cavities located relatively closely on one side of the cylinder, with the intake valve positioned above the exhaust valve. The valves have a parallel orientation relative to the piston bore, with their heads and seats located near the head of the cylinder in communication with the piston bore and the spark plug. The intake valve periodically opens to create a passageway connecting a carburetor and the piston bore, with the passageway including the intake cavity near the cylinder head. Similarly, the exhaust valve periodically opens a passageway connecting the piston bore and an exhaust system, which includes a muffler, with the passageway including an exhaust cavity near the cylinder head. A common camshaft located within the crankcase lifts and opens the valves.
Although the intake and exhaust valves are disposed on a common side of the cylinder, locating the carburetor and the exhaust system on opposite sides of the engine provides a number of benefits. One benefit is that the carburetor is not exposed to the exhaust heat from the exhaust system, which minimizes negative consequences which result when the carburetor is excessively heated. Another benefit relates to separating the carburetor fuel lines from the muffler to avoid the potential hazard from having the fuel too close to a heat source.
To achieve these and other benefits, prior art engines route an external intake tube from the intake value, over the cylinder, to the carburetor located on the opposite side. Locating the intake valve above the exhaust valve results in less efficient cooling of the exhaust because the exhaust cavity is less exposed to the flow of cooling air which circulates more about the upper sections of the engine. In addition, the intake system insulates the exhaust system, inhibiting the dissipation of heat because the rising heat from the exhaust system is trapped by the components of the intake system. Further, routing the intake tube over the cylinder requires that the carburetor be mounted relatively high with respect to the mounting of the engine. This restricts the space available above the carburetor to accommodate a gravity feed fuel tank, constraining the volume of the tank if the height of the engine is unchanged. Alternatively, a larger fuel tank can be provided, but that requires the undesirable result of increasing the height of the engine.
A solution of the aforementioned problems involves routing the intake passageway, formed within the cylinder block, under the cylinder, as disclosed in the co-pending application entitled "Engine Cylinder Assembly Having An Intake Cross-Passageway", Ser. No. 342,186, filed Apr. 24, 1989, now U.S. Pat. No. 4,893,597. This arrangement allows for better ventilation for the exhaust system while not restricting the space available for a fuel tank. However, providing an integrally formed intake passageway within the cylinder entails extra manufacturing steps and cost. Also, the intake system buried within the block absorbs heat from the block, reducing the overall volumetric efficiency.
What is needed in the art is an engine that realizes the advantages of a cross-under intake passageway underneath the cylinder while a minimizing the cost and without absorbing the excess heat which reduces the efficiency.